This invention relates to a method for labeling an explosive medium with a readily identifiable, coded indicator which can be utilized to identify the explosive after its detonation. In a more particular aspect this invention concerns itself with the coded tagging of explosives for post-detonation identification and the ready identification and retrieval of a color-coded taggant from a detonated explosive medium.
Preventing and controlling the illegal use of explosives has become a problem of paramount importance for law enforcement, regulatory and other government agencies. As a consequence, a considerable research effort has been under taken in an attempt to provide means and methods for detecting and identifying explosives both before and after their detonation. Considerable success has been achieved and a number of labeling and tracing methods have evolved for identifying many explosives. For example, the use of microparticles having a combination of coded tagging elements incorporated within the body of the microparticle is shown in U.S. Pat. No. 3,772,200. Tagging explosives with organic particles is shown in U.S. Pat. No. 3,897,284 while U.S. Pat. No. Re. 29,334 illustrates the use of phosphors for providing explosives with a distinctive information level. These methods, however, suffer certain disadvantages because of difficulty in retrieving and identifying the coded materials. Oftentimes they require expensive and complicated analytical equipment in order to "read" the code.
Another method for identifying explosives, however, has been demonstrated by the 3M Company and includes the use of a multilayered color-coded microparticle. U.S. Pat. No. 4,053,433 illustrates this concept. This patent also suggests the use of a fluorescent color in the color code and the incorporation of magnetic oxide or iron particles in the taggant to facilitate retrieval of the color-coded microparticle for identification through the use of a microscope or magnifying glass. Unfortunately, the utilization of a magnetic substance permits the removal of the taggant prior to detonation thereby subverting the original purpose of using the taggant as an identification aid. Unscrupulous individuals, with the aid of a strong magnet, could easily remove the color-coded taggants from a granular explosive, e.g. smokeless or black powder.
In accordance with the present invention, however, the early or pre-detonation removal of magnetic susceptible taggants has been solved by replacing the magnetic material with a compound that is rendered magnetic only after detonation of the explosive. Before detonation this material is non-magnetic and only develops its magnetic properties under the effects of shock and fireball heating that occur during detonation of the explosive.